Table 5

Odds ratios for developing ACPA-positive RA and ACPA-negative RA in subjects exposed
to different combinations of smoking and presence of HLA-DRB1*04:05 or non-HLA-DRB1*04:05 SE alleles, compared with never-smokers without SE alleles in MyEIRA

No SE alleles

HLA-DRB1*04:05 SE allelesab

Any non-HLA-DRB1*04:05 SE allelesc

Ca/Co

OR (95% CI)

Ca/Co

OR (95% CI)

Ca/Co

OR (95% CI)

ACPA-positive RA

Never-smokers

266/986

1.0

102/71

5.4 (3.8 to 7.5)

152/130

3.1 (2.4 to 4.0)

Ever-smokers

30/52

3.1 (1.7 to 5.7)

16/7

12.9 (4.7 to 35.3)

15/1

82.4 (10.3 to 656.9)

AP

0.4 (-0.1 to 0.9)

0.9 (0.8 to 1.1)

ACPA-negative RA

Never-smokers

254/986

1.0

20/71

1.1 (0.7 to 1.8)

44/130

1.3 (0.9 to 1.9)

Ever-smokers

10/52

0.6 (0.2 to 2.0)

1/7

0.6 (0.1 to 4.8)

2/1

8.1 (0.7 to 93.0)

ACPA, anti-cyclic citrullinated proteins antibody; AP, attributable proportion due
to interaction; Ca/Co, number of exposed cases/number of exposed controls; MyEIRA,
Malaysian Epidemiological Investigation of Rheumatoid Arthritis; OR (95% CI), odds
ratio and 95% confidence interval, adjusted for ethnicity, formal education, age,
sex, residential area, calculated by means of unconditional logistic regression to
increase power; RA, rheumatoid arthritis; SE, shared epitope. a HLA-DRB1*04:05 group was defined by the presence of either one or two copies of HLA-DRB1*04:05 allele. bIndividuals with first allele of HLA-DRB1*04:05 and second allele of a non-HLA-DRB1*04:05 SE (that is, HLA-DRB1*04:05/non-HLA-DRB1*04:05 SE) were not included in the interaction analysis (cases, 13; control, 1). cAny non-HLA-DRB1*04:05 SE alleles group was defined by the presence of either one or two copies HLA-DRB1*01:01, *01:02, *01:07, *04:01, *04:04, *04:08, *04:10, *10:01, and *10:03 alleles.